In general, vehicle drivelines transmit torque from a vehicle's engine to its wheels. Automotive drivelines sometimes include power transfer units (PTUs) for selectively distributing torque among shafts in the drivelines. The PTUs are often equipped in four-wheel drive and all-wheel drive (AWD) automotive driveline configurations. A power transfer unit typically consists of a housing that encloses and supports gears, shafts, bearings, as well as other components.
Sometimes PTUs are capable of disconnecting and re-connecting its components. The disconnected components are no longer driven to rotate and no longer transmit torque between them. These capabilities, along with other disconnected components in automotive drivelines, can preclude driven rotations in portions of the drivelines not needed to transmit torque at a particular time. For instance, on-demand AWD automotive driveline configurations do not always transmit torque among all of its shafts. Increased fuel mileage, reduced emissions, and other performance improvements often result.